The neuroanatomy of memory encompasses a wide variety of anatomical structures in the brain.
Subcortical structures
Hippocampus
The hippocampus is a structure in the brain that has been associated with various memory functions. It is part of the limbic system, and lies next to the medial temporal lobe. It is made up of two structures, the Ammon's Horn, and the Dentate gyrus, each containing different types of cells.
Cognitive maps There is evidence that the hippocampus contains cognitive maps in humans. In one study, single-cell recordings were taken from electrodes implanted in a rat's hippocampus, and it was found that certain neurons responded strongly only when the rat was in certain locations. These cells are called place cells, and collections of these cells can be considered to be mental maps. Individual place cells do not only respond to one unique area only however, the patterns of activation of these cells overlap to form layered mental maps within the hippocampus. A good analogy is the example of the same television or computer screen pixels being used to light up any trillions of possible combinations to produce images, just as the place cells can be used in any multiple possible combinations to represent mental maps. The hippocampus' right side is more oriented towards responding to spatial aspects, whereas the left side is associated with other context information. Also, there is evidence that experience in building extensive mental maps, such as driving a city taxi for a long time (since this requires considerable memorization of routes), can increase the volume of one's hippocampus.
Encoding Damage to the hippocampus and surrounding area can cause anterograde amnesia, the inability to form new memories. This implies that the hippocampus is important not only for storing cognitive maps, but for encoding memories.
The hippocampus is also involved in memory consolidation, the slow process by which memories are converted from short to long term memory. This is supported by studies in which lesions are applied to rat hippocampi at different times after learning. The process of consolidation may take up to a couple years.
It has also been found that it is possible to form new semantic memories without the hippocampus, but not episodic memories, which means that explicit descriptions of actual events (episodic) cannot be learned, but some meaning and knowledge is gained from experiences (semantic).
Cerebellum
The cerebellum ("little brain") is a structure located at the rear of the brain, near the spinal cord. It looks like a miniature version of the cerebral cortex, in that it has a wavy, or convoluted surface.
Unlike the hippocampus which is involved in the encoding of complex memories, the cerebellum plays a role in the learning of procedural memory, and motor learning, such as skills requiring co-ordination and fine motor control. An example of a skill requiring procedural memory would be playing a musical instrument, or driving a car or riding a bike. Individuals with transient global amnesia that have difficulty forming new memories and/or remembering old events may sometimes retain the ability to perform complex musical pieces, suggesting that procedural memory is completely dissociated from conscious memory, also known as explicit memory.
This separation makes sense if the cerebellum, which is far removed from the hippocampus, is responsible for procedural learning. The cerebellum is more generally involved in motor learning, and damage to it can result in problems with movement, specifically it is considered to co-ordinate timing and accuracy of movements, and to make long-term changes (learning) to improve these skills.
Amygdala
Located above the hippocampus in the medial temporal lobes are two amygdalae (singular "amygdala"). The amygdalae are associated with both emotional learning and memory, as it responds strongly to emotional stimuli, especially fear. These neurons assist in encoding emotional memories and enhancing them. This process results in emotional events being more deeply and accurately encoded into memory. Lesions to the amygdalae in monkeys have been shown to impair motivation, as well as the processing of emotions.
Memory of fear conditioning Pavlovian conditioning tests have shown the active role of the amygdala in fear conditioning in rats. Research involving lesions to the basolateral nucleus have shown a strong association with memories involving fear. The central nucleus is linked with the behavioral responses that are dependent on the basolateral's reaction to fear. The central nucleus of the amygdala is also linked to emotions and behaviors motivated by food and sex.
Memory consolidation Emotional experiences and events are somewhat fragile and take a while to be completely set into memory. This slow process, referred to as consolidation, allows emotions to influence the way the memory is stored.
The amygdala is involved in memory consolidation, which is the process of transferring information that is currently in working memory into ones long-term memory. This process is also known as memory modulation. The amygdala works to encode recent emotional information into memory. Memory research has shown that the greater ones emotional arousal level at the time of the event, the greater the chance that the event will be remembered. This may be due to the amygdala enhancing the emotional aspect of the information during encoding, causing the memory to be processed at a deeper level and therefore, more likely to withstand forgetting.
Basal ganglia and motor memory
The basal ganglia are a group of nuclei which are located in the medial temporal lobe, above the thalamus and connected to the cerebral cortex. Specifically, the basal ganglia includes the subthalamic nucleus, substantia nigra, the globus pallidus, the ventral striatum and the dorsal striatum, which consists of the putamen and the caudate nucleus. The basic functions of these nuclei deal with cognition, learning, and motor control and activities. The basal ganglia are also associated with learning, memory, and unconscious memory processes, such as motor skills and implicit memory. Particularly, one division within the ventral striatum, the nucleus accumbens core, is involved in the consolidation, retrieval and reconsolidation of drug memory.
The caudate nucleus is thought to assist in learning and memory of associations taught during operant conditioning. Specifically, research has shown that this part of the basal ganglia plays a role in acquiring stimulus-response habits, as well as in solving sequence tasks.
Damage to the basal ganglia has been linked to dysfunctional learning of motor and perceptual-motor skills. Most disorders that are associated with damage to these areas of the brain involve some type of motor dysfunction, as well as trouble with mental switching between tasks in working memory. Such symptoms are often present in those who suffer from dystonia, athymhormic syndrome, Fahr's syndrome, Huntington's disease or Parkinson's disease. Huntington's and Parkinson's disease involve both motor deficits and cognitive impairment.
Cortical structures
Frontal lobe The frontal lobes are located at the front of each cerebral hemisphere and positioned anterior to the parietal lobes. It is separated from the parietal lobe by the primary motor cortex, which controls voluntary movements of specific body parts associated with the precentral gyrus.Kuypers, H. (1981). Anatomy of the descending pathways. V. Brooks, ed. The Nervous System, Handbook of Physiology, vol. 2. Baltimore: Williams and Wilkins. The cortex here serves our ability to plan the day, organize work, type a letter, pay attention to details and control the movements of your arms and legs. It also contributed to your personality and behaviour.
When considering the frontal lobes in regards to memory, we see that it is very important in the coordination of information. Therefore, the frontal lobes are important in working memory. For example, when you are thinking about how to get to a mall you have never been to before, you combine various bits of knowledge you already have: the layout of the city the mall is in, information from a map, knowledge of traffic patterns in that area and conversations with your friends about the location of the mall. By actively using all of this information, you can determine the best route for you to take. This action involves the controlled use of information in working memory, coordinated by the frontal lobes.
The frontal lobes help a person select out memories that are most relevant on a given occasion. It can coordinate various types of information into a coherent memory trace.Frankland P.W., Bontempi B. (2005). The organization of recent and remote memories. Nat. Rev. Neurosci. 119–130. For example, the knowledge of the information itself, as well as knowing where information came from must be put together into a single memory representation; this is called source monitoring. Sometimes we experience situations where information becomes separated, such as when we recall something, but cannot remember where we remember it from; this is referred to as a source monitoring error.
The frontal lobes are also involved in the ability to remember what we need to do in the future; this is called prospective memory.Winograd, E. (1988). Some observations on prospective remembering. In M. M. Gruneberg, P. E. Morris & R. N. Sykes (Eds.), Practical Aspects of Memory: Current Research and Issues. Vol. 2, pp. 348-353.
Temporal lobe The temporal lobes are a region of the cerebral cortex that is located beneath the Sylvian fissure on both the left and right hemispheres of the brain. Lobes in this cortex are more closely associated with memory and in particular autobiographical memory.
The temporal lobes are also concerned with recognition memory. This is the capacity to identify an item as one that was recently encountered. Recognition memory is widely viewed as consisting of two components, a familiarity component (i.e. Do I know this person waving at me?) and a recollective component (i.e. That is my friend Julia, from evolutionary psychology class).
Damage to the temporal lobe can affect an individual in a litany of ways ranging from: disturbance of auditory sensation and perception, disturbance of selective attention of auditory and visual input, disorders of visual perception, impaired organization and categorization of verbal material, disturbance of language comprehension, and altered personality.
In regard to memory, temporal lobe damage can impair long-term memory.Kolb, B., & Whishaw, I. (1990). Fundamentals of Human Neuropsychology. W.H. Freeman and Co., New York. Thus, general semantic knowledge or more personal episodic memories of one's childhood could be affected.
Parietal lobe The parietal lobe is located directly behind the central sulcus, superior to the occipital lobe and posterior to the frontal lobe, visually at the top of the back of the head.Blakemore & Frith (2005). The Learning Brain. Blackwell Publishing. The make up of the parietal lobe is defined by four anatomical boundaries in the brain, providing a division of all the four lobes.